This application is based on Japanese Patent Application No. 09-086157 filed on Apr. 4, 1997, No. 09-086158 filed on Apr. 4, 1997, and No. 09-086159 filed on Apr. 4, 1997, the contents of which are incorporated herein by reference.
1. Field of the Invention
This invention relates to an image processor in which a mixture of various images appearing in an original document and respectively having different attributes such as dots, characters and photographs can be adequately subjected to image processing in accordance with the respective attributes of images. This invention will be found particularly advantageous when used in a digital copying machine.
2. Description of the Prior Art
In reproducing an original document of the kind indicated above, it has been found extremely desirable to process various images in accordance with the attributes of respective images.
For this purpose, it is essential that a plurality of regions appearing in an original document and respectively having images different in attributes be correctly determined and discriminated from each other.
It is known to determine the attribute of each picture element on the basis of a difference in photographic density, on the basis of a difference between the highest photographic density and the lowest photographic density, or on the basis of information obtained from a histogram illustrating the distribution of photographic densities. It is also known to determine the attribute of one region on the basis of spatial frequency spectra. A neural information processing system has been used heretofore for the purpose of such determination.
Misjudgment is likely to occur in the aforesaid known methods, because they involve the determination of each picture element in an image or the determination of a small region from other small regions.
More specifically stated, a region actually occupied by a single attribute is likely to be mistaken for a region in which a plurality of attributes lie adjacent to one another. Deteriorated picture quality will be caused by image processing based on such misjudgment.